The man, Constantin Tshidime Bulabula, will be brought before a military court in Kananga, Brig. Gen. Marcellin Assoumani Issa Kumba of the Congolese armed forces said.

Mr. Bulabula had been sought since he disappeared from his home in October.

The experts, Michael Sharp, 34, an American, and Zaida Catalán, 36, a Swede, were investigating crimes associated with a rebellion in central Kasai Province when they were abducted along with four Congolese colleagues in March 2017.

The bodies of Mr. Sharp and Ms. Catalán were found two weeks later, about 75 miles south of Kananga. The whereabouts of their colleagues are unknown.

Human rights groups have suspected the government may have played a role in the killings, and a United Nations inquiry in August could not rule out government involvement. Video footage of Congolese troops killing civilians in Kasai has led to at least seven arrests.

The Congolese army has denied involvement in the experts’ killing. In April, the government released a video that it said documented the execution of the two experts. It identified the executioners as members of the Kamwina Nsapu militia.

The authorities say Mr. Bulabula is a member of the militia, which took up arms against Congolese security forces after the death of its leader in mid-2016. As many as 5,000 people have died in the fighting that has followed, and the United Nations has identified mass graves scattered across the province.

“We did our job and we found the person who was implicated in the murder case of the experts,” Justin Milonga, acting governor of Kasai Central, said of Mr. Bulabula’s arrest. “Let justice do its job.”